The present invention relates to a method and apparatus for wrapping groups of products with stretch film, where the grouped products are bottles with bases of different shapesxe2x80x94for example, circular, square or rectangularxe2x80x94or even containers made of metal (including parallelepiped shaped containers).
In conventional production lines where the production process includes the wrapping of groups of plastic bottles (to which the present description will hereinafter refer, although the invention may also be applied to other types of product or container), the final wrapping over the groups of bottles usually consists of a sheet of heat-shrink material.
In some cases and for some types of products, these lines may, however, be very expensive for the manufacturer because they have numerous operating units, such as product collating units (especially in the case of continuous lines), and film feed and heating units, all of which require a high number of control devices and accessory parts, not to mention the high cost of the heat shrink film itself. Another limiting factor on production lines of this kind is the fact that some products cannot be heated beyond certain limits, which means that heat shrink wrapping solutions are not feasible.
The teachings of prior art also include more economical wrapping solutions adopted instead of heat shrink wrapping methods and machines, but providing standards of quality that are at least as high as those provided by heat shrink wrapping solutions.
One of these alternative solutions is described in patent IT 1.285.827, in the name of the same Applicant as the present. In this solution, a tubular portion of stretch film, that is to say, elastically extensible film, is used in a method where the portion of film is fed by a film feed station and then stretched transversally by a plurality of rods. In this way, the size of the tubular portion of film is enlarged so that its transversal dimension is increased from a minimum size to a size greater than the front of the groups of products. The rods then align the film with the line of product feed so as to enable a single group of products to move into the stretched tube of film. The rods, moving in synchrony with the feed motion of the groups of products, then release the tube of film allowing it to shrink to its former size in such a way that it envelops the package.
This wrapping method is extremely practical, fast and economical compared to heat shrink wrapping methods and its use is currently preferred for many type of productsxe2x80x94whether bottles or other containersxe2x80x94to be wrapped with film.
Consequently, the demand for stretch wrapping has increased considerably. This has been accompanied by a corresponding increase in the need to change some of the steps in the stretch wrapping process and the structure of stretch wrapping equipment which, at present, is cumbersome and takes up a large amount of factory space.
Starting from the wrapping method briefly described above and through continual research and development, the Applicant has invented a new method for wrapping groups of products with stretch film. The new method is extremely fast and provides a very strong, high-quality end package.
The invention also has for an object to provide an apparatus that implements this method and that is compact, fast and very reasonably priced.
Accordingly, the present invention provides a method for wrapping groups of products with stretch film comprising the following steps: forming groups of products having a front and a longitudinal dimension that follows a line of feed; winding a stretch film unrolled from a first roll around first means for preforming the wrapping, positioned inside a film wrapping area and along the product group line of feed; forming a first tubular portion of stretch film; stretching the portion of film by moving the first preforming means to create an access area for a single group of products moving along the feed line, the transversal dimension of the access area being larger than the front of the group of products; releasing the portion of stretch film to allow the film to shrink to its former size over the group of products and thus wrapping it; expelling the wrapped package thus obtained onto the feed line.